This invention relates to a process for obtaining cold water infusible or extractable tea and to the products obtained thereby that have good colour and flavour.
Leaf tea may be prepared as green leaf tea or black leaf tea. Generally, to prepare black leaf tea fresh green leaves of the plant Camellia sinensis are withered (subjected to mild drying), comminuted, fermented (in which process enzymes in the tea leaf use atmospheric oxygen to oxidise various substrates to produce brown-coloured products) and then fired (to dry the tea leaves). Green leaf tea is not exposed to the fermentation process. Partial fermentation may be used to produce intermediate-type teas known as xe2x80x9coolongxe2x80x9d tea.
Tea is consumed as a hot beverage or a cold beverage such as iced tea. The numerous compounds in the leaves that give the beverage its unique organoleptical properties are only sparingly soluble in cold water so tea is usually infused in water at temperatures close to 100xc2x0 C. When iced tea is desired the tea is infused in water at about 100xc2x0 C. and then chilled in a refrigerator for example until it is cold. Unfortunately this can take several hours.
Once can prepare iced tea by dissolving the spray dried liquor obtained at high temperature from black tea or fibres generated during black tea manufacturing process in cold water.
U.S. Pat. No. 4,051,264 (Lipton/Sanderson) discloses a method for making a cold water soluble leaf tea extract. Tea leaves are pre-treated with tannase under anaerobic conditions to generate a cold-water infusing tea with good colour, yield and flavour.
U.S. Pat. No. 3,812,266 (Sanderson/Coggon) discloses a method that involves converting green tea to black using tannase and natural tea enzymes. The method also includes a tannase pre-treatment step, but in a slurry system, followed by oxidation by natural tea enzymes to convert green tea into black, and generate tea powders, which are both hot and cold water soluble.
The article by Tadao Kurata et al in Agr. Biol. Chem, 37 (6), 1471-1477, 1973 discloses that a red pigment is produced at the initial stage of the browning reaction of dehydro-L-ascorbic acid (DHA) with alpha-amino acid. 5-phenyl-3,4-diketo-gamma-butyrolactone, which has the same type of lactone ring structure as dehydro-L-ascorbic acid, is said to give a similar red colour when reacted with alpha-amino acid. The pigment is said to have the same structure as the red pigment that is produced by the oxidation of L-scorbamic acid.
Tannase is an expensive enzyme and is also not legally cleared in several countries for usage in tea. In any event, while this is convenient, for many consumers the quality of the final beverage is not equal to that prepared from hot infused leaves. Some consumers prefer not to use powders as they perceive them to be artificial, unnatural and simply lacking in the romance of taking tea.
There is therefore a need for a leaf tea that yields acceptable tea flavour and colour when infused in cold water.
The present inventors have now found that one can prepare a black leaf tea that provides a high quality tea beverage when infused in hot or cold water by treating tea leaves with one or more of ascorbic acid, dehydroascorbic acid, 1-scorbamic acid or 5-phenyl-3,4-diketo-gamma-butyrolactone (4-phenyl-2,3-diketo-gamma-butyrolactone) or their salts during black tea manufacture.
The present invention can be said in broad terms to relate to a process for manufacturing a cold water soluble black leaf tea comprising the steps of macerating freshly plucked tea leaves, allowing them to ferment, firing the leaves to arrest fermentation and then drying them to yield black leaf tea, the process being characterised in that the tea leaves are treated with a solubilising compound selected from the group consisting of ascorbic acid, dehydroascorbic acid, 1-scorbamic acid, 5-phenyl-3,4-diketo-gamma-butyrolactone or their salts and mixtures thereof in an amount that is sufficient for the black leaf tea to be soluble in water at 5 to 100xc2x0 C.
The tea leaves are preferably treated with the solubilising compound in the presence of oxidative enzymes and/or hydrogen peroxide to enhance the tea flavour and colour.
xe2x80x9cTeaxe2x80x9d for the purposes of the present invention means leaf material from Camellia sinensis var. sinensis or Camellia sinensis var. assamica. It also includes rooibos tea obtained from Aspalathus linearis however that is a poor source of endogenous fermenting enzymes. xe2x80x9cTeaxe2x80x9d is also intended to include the product of blending two or more of any of these teas.
xe2x80x9cLeaf teaxe2x80x9d for the purposes of this invention means a tea product that contains one or more tea origins in an uninfused form.
xe2x80x9cCold water solublexe2x80x9d for the purposes of this invention means giving good colour, flavour and mouthfeel in a short infusion time i.e. less than 10 minutes, but preferably less than 5 minutes at a temperature at or above 5xc2x0 C.
For the avoidance of doubt the word xe2x80x9ccomprisingxe2x80x9d is intended to mean including but not necessarily xe2x80x9cconsisting ofxe2x80x9d or xe2x80x9ccomposed ofxe2x80x9d. In other words the listed steps or options need not be exhaustive.
Tea manufacture, especially black tea manufacture, traditionally comprises: withering, macerating, fermenting and firing. Black tea for the purpose of the invention is obtained by the following process.
Withering is a process whereby the plucked tea leaves are stored for periods of time (perhaps up to 24 hours), during which they undergo various biochemical and physical changes which often includes a loss of moisture. It is optional but preferred.
Maceration follows the withering step, and traditionally the withered leaves are optionally rolled to bruise and crush the leaves i.e. break down the plant tissue structure. This will have the effect of liberating fermentable substrates and fermenting enzymes from within the plant cells and tissue. Modern tea manufacture usually includes this step however the plant cells and tissue is broken down by passing tea, which has usually been withered, through a cutting machine. Thus for the purpose of the invention the green tea leaves may be macerated using a CTC, ball mill or a grinder or a hammer mill or a LAWRI(trademark) tea processor or a LEGG(trademark) cutting machine or rolled using tea rollers as in orthodox tea processing.
The next step is commonly called fermentation but that is a misnomer. xe2x80x9cFermentationxe2x80x9d is commonly used in the context of brewing alcohol to describe the action of exogenous enzymes. However in the tea world it is used to refer to the oxidative and hydrolytic process that tea undergoes when certain endogenous enzymes and substrates are brought together by mechanical disruption of the cells by macerating of the leaves. During this process colourless catechins in the leaves are converted to a complex mixture of yellow and orange to dark-brown substances and producing a large number of aromatic volatile compounds.
The fermented product is fired and dried to give a black leaf tea. The firing involves heating and drying the tea to destroy the fermenting enzymes and thereby arrest fermentation. It results in a reduction of moisture content to below 5%, and also leads to further chemical oxidation and changes in tea aroma. This generally involves exposing the tea to a blast of hot, dry air in a dryer.
The present invention concerns a modification to traditional black tea manufacture. The modification involves treating the tea leaves with a solubilising compound selected from the group consisting of ascorbic acid, dehydroascorbic acid, 1-scorbamic acid, 5-phenyl-3,4-diketo-gamma-butyrolactone or their salts and mixtures thereof in order to enhance the solubility of the black tea in cold water.
The solubilising compound 5-phenyl-3,4-diketo-gamma-butyrolactone referred to in the aforementioned article in Agr. Biol. Chem, 37 (6), 1471-1477, 1973 by Tadao Kurata et al has oxygen at the 1 position as is common when labelling heterocyclic compounds. However this compound can also be labelled as 4-phenyl-2,3-diketo-gamma-butyrolactone, wherein the keto groups are at the 2 and 3 positions and the phenyl group is at the 4 position.
The tea leaves are treated with the solubilising compound post plucking, preferably prior to an optional but preferable withering step. The withering step, if desired, preferably tales 1 to 24 hours at 10 to 40xc2x0 C.
The compounds are preferably in the form of a solution at a concentration of from 0.5 to 10% by weight of tea. The solubilising compound can be applied singly or in split doses. The treatment is preferably given in the form of a spray or dip.
The tea is preferably fermented for 10 minutes to 3 hours at 10 to 60xc2x0 C.
It is particularly preferred to provide additional oxidative enzymes and hydrogen peroxide along with the above treatment to enhance the generation of colour and flavour.
The oxidative enzymes may be selected from polyphenol oxidase, tyrosinase and peroxidase of bacterial, fungal or plant origin at concentrations ranging from 2000 to 100000 units per gram on the basis of made black tea and hydrogen peroxide at concentrations ranging from 0.01 to 1% on the basis of made black tea
The tea can be dried using any art-known means, preferably giving leaf tea with a moisture content of less than 5%.
The products obtained by the above process can be used to produce instant tea or for infusing black tea in water at temperatures in the range of 5 to 100xc2x0 C. The instant tea can be produced by extracting the tea leaves produced by the above process with boiling water, clarifying the extract, and drying it. The instant tea produced by this method will give higher yields of cold water soluble tea solids having superior tea colour and flavour than the instant tea produced by the conventional methods. Water infusions of the tea produced by the process described above in water at temperatures in the range of 5 to 100xc2x0 C. will give tea with superior colour and flavour.
A first preferred embodiment of the process of the invention comprises the steps of:
(a) macerating green tea leaves optionally after withering for 1-24 hours;
(b) processing the macerated tea in a conventional manner to obtain black tea, wherein the green tea is treated with at least one of ascorbic acid, dehydroascorbic acid, 1-scorbamic acid, 5-phenyl-3,4-diketo-gamma-butyrolactone (4-phenyl-2,3-diketo-gamma-butyrolactone) or their salts in single or split doses at a concentrate of 0.5 to 10% by wt. of tea selectively prior to maceration and/or during maceration and/or the post maceration stages of the above processing of tea depending upon the quality of the infusibility desired;
(c) fermenting the macerated tea optionally up to 3 hours at temperature of 10 to 60xc2x0 C.; and
(d) processing the tea in a conventional manner to obtain black tea.
A second preferred embodiment of the process of the invention comprises the steps of:
(a) macerating the green tea leaves that has been optionally withered for 1-24 hours;
(b) treating the macerated green tea with one or more of ascorbic acid, dehydroascorbic acid, 1-scorbamic acid or 5-phenyl-3,4-diketo-gamma-butyrolactone (4-phenyl-2,3-diketo-gamma-butyrolactone) or their salts in single or in split doses, at a concentration 0.5 to 10% by weight of made tea;
(c) fermenting the macerated, treated tea for 10 minutes to 3 hours at a temperature of 10 to 50xc2x0 C.; and
(d) processing the material in a conventional manner to obtain black tea.
A third preferred embodiment of the process of the invention comprises the steps of:
(a) macerating the green tea leaves that has been optionally withered for 1 to 24 hours at 10 to 40xc2x0 C.;
(b) treating the macerated mass with one or more of ascorbic acid, dehydroascorbic acid, 1-scorbamic acid or 5-phenyl-3,4-diketo-gamma-bytyrolactone (4-phenyl-2,3-diketo-gamma-butyrolactone) or their slats in single or in split doses, at a concentration 0.5 to 10% by weight of made tea;
(c) fermenting the macerated, treated tea for 10 minutes to 3 hours at a temperature of 10 to 50xc2x0 C.; and
(d) drying the material at 90 to 180xc2x0 C. to obtain black tea with a moisture content less than 5%.
A fourth preferred embodiment of the process of the invention comprises the steps of:
(a) macerating the green tea leaves that has been optionally withered for 1 to 24 hours at 10 to 40xc2x0 C.;
(b) treating the macerated mass with one or more of ascorbic acid, dehydroascorbic acid, 1-scorbamic acid or 5-phenyl-3,4-diketo-gamma-butyrolactone (4-phenyl-2,3-diketo-gamma-butyrolactone) or their slats in single or in split doses, at a concentration 0.5 to 10% by weight of made tea in the presence of additional oxidative enzymes and hydrogen peroxide;
(c) fermenting the macerated, treated tea for 10 minutes to 3 hours at a temperature of 10 to 50xc2x0 C.; and
(d) drying the material at 90 to 180xc2x0 C. to obtain black tea with a moisture content less than 5%.
The process of the invention shall now be described with reference to the following example: